When a panel of this type is used for exchanging heat with a soot-laden gas (such as the gas from incinerating papermaking black liquor or household waste) flowing outside the tubes, and particularly when the tubes are spaced at a pitch (distance between the tube axes) which is relatively large (e.g. twice the tube diameter), deposits of soot build up fairly rapidly between the tubes. These deposits reduce the heat exchange coefficient and sometimes cause heavy corrosion of the tubes, and they are difficult to remove by steam-jet sweeping.
To remedy these difficulties, panels of tubes have been used in which the spacing is very small (with the pitch being only a few mm greater than the tube diameter), by holding the tubes to one another by means of small rings welded from place to place therebetween. Such panels are easier to clean, but this disposition requires numerous manual welds, and these welds do not stand up over long periods of time to the stresses due to temperature differences between the tubes and to forces acting on the panels. The welds then given rise to cracks and leaks from the tubes.
Published French patent specification No. 1 418 565 describes a heat exchanger panel in which the tubes are close to one another and are interconnected by fins. The welds between fins and the end tubes suffer similarly from stresses due to temperature differences between tubes and to the weight of the central portion of the panel, and are therefore also likely to give rise to cracks and leaks from the tubes.
Preferred embodiments of the present invention provide a panel for exchanging heat with a soot-laden gas, which panel is easy to clean of soot deposits, and is simultaneously easy to manufacture, is capable of mechanized manufacture, and does not have weaknesses at the welds.